Torque amplifying system



March 18, 1952 N. MINORSKY TORQUE AMPLIFYING SYSTEM Filed OOC. 26, 1.945

Patented Mar. 18, 1952 TORQUE AMPLIFYING SYSTEM Nicholas Minorsky, Bethesda, Md., assigner, by mesne assignments, to Lear, Incorporated, Grand Rapids, Mich., a corporation of Illinois Application October 26, 1945, Serial No. 624,772

10 Claims. l

This invention relates to torque amplifying devices, and more particularly to such arrangements in which a relatively small force or torque is proportionately ampliiied. Regarded in one aspect the invention has for a principal object the provision of a steering gear for a dirigible craft capable of the advantages of a purely manual control of the rudder while utilizing force 'amplification in the operation thereof.

Purely manual control as alluded to in the foregoing paragraph is intended to mean those cases wherein the rudder is connected directly to a steering wheel by cables in the simple, conventional manner without the interposition of an auxiliary source of power such as asteering engine provided with a follow-up attachment. With the foregoing type of control the helmsman, when he desires to turn the ship, rotates the steering wheel, applying a gradually increasing effort as the rudder angle increases. Lf the helmsman, after having introduced a selected rudderangle, removes his hands from the wheel,

the hydrodynamic pressure of the water particles on the rudder tends to return the rudder to its middle position, and since the rudder is directly connected to the steering wheel, the latter likewise returns to its middle position. Obviously the situation just recited fails to exist where there is provided a steering engine including a follow-up attachment. In this case, if the helmsman, after having introduced a predetermined rudder angle, removes his hands from the wheel, the rudder does not spontaneously return to its middle position. Such end can be brought about only by movement of the Wheel to its middle position by the helmsman. For this reason, installations including a steering engine must be ,provided with a rudder angle indicator as the helmsman is without feel as to the then existing rudder angle.

Having pointed out the signincance of the is well-known that if a few turns of a cable are` wrapped around a cylindrical drum with some initial tension, i. e. not loosely, and both ends of y the cable are secured to suitably xed points, a

subsequent steady rotation of the drum with incident slipping of the cable on the drum surface,

will produce a substantial difference in the ten- A tion of the two ends of the cable. If it is agreed to dene that end of the cable toward which the surface of the drum is caused to rotate as the input end, and that end away from which the drum surface is rotating as the output end, and specify that the respective different cable tensions as f and F it is easy to show that F :feLa

where ,c is the coeiicient of friction of the cable with respect to the drum, a is the angle over which the cable is wrapped, and e is the base of natural logarithme. Since the exponential function is always greater than unity, and, for a sumciently large value or the exponent may be made a very large number, it follows that F may be made many times greater than f. The principle just outlined is utilized in the invention system.

If, instead of referring to the forces F and f, one considers the moments of such forces about the axis of the drum, the foregoing discussion may be referred to equally as torque amplification.

Moreover, if, in lieu of securing the ends of the cable iixed supports, these ends are connected to elements of a system to which forces can be applied it will be clear that a small force at the input end can be effective to yield a much larger force at the output end, the two forces always being in the ratio epa: f

It will also be apparent that if the points at which the respective forces act are free to move there will exist power amplication as well, and that the power amplication will have a value y equal to the ratio of the forces or of the torques.

Such increase in power at the output end will be supplied by the source used to rotate the drum.

Now turning to the invention arrangement, the drum, instead of being connected rigidly and constantly to a power source, is driven through a clutch, preferably of the slipping disc type. In some well-known forms of such clutches the magnitude of the pull-out torque is substantially proportional to the pressure with which the clutch discs are held in contact, and such pressure may be produced by an electro-magnet having an armature to which one disc is secured, for example, as disclosed in United States Letters Patent No. 2,267,114, granted to William P. Lear on December 23, 1941. Since the pressure with which the clutch discs are held in Contact is substantially proportional to the exciting current, it is possible, by controlling the latter, to control the transmitted torque. In the invention system means are provided for controlling the clutch excitation current in response to the tension prevailing in the input end of the cable. Accordingly I provide, in the input end of the cable, a tension-measuring device which is effective in turn to control the electrical input to the clutch coil. The arrangement is such that for a large input tension the exciting current is large. Under this condition the drum will be rotated, the above-mentioned relation between the forces f and F will be established, and the force F will 1,

moved entirely, corresponding to the reduction or absence of force exerted by the helmsm'an Vin the manual case, the drumbecomes free andthe forces f and F disappear. Accordingly the only force acting on the wheel'isthe hydrodynamic reaction on the rudder. Thus such reaction will restore the rudder to streamline position, i. e.,

stable equilibrium, and likewise the steering Wheel.

The invention is particularly applicable to installations in which a relatively small manual control force is applied to control a relatively'large power force in correspondence therewith. Typical examples of such systems .are .power steering systems for water borne vessels and aircraft, industrial applications such as cranes .and hoists, and other similar arrangements. In many installations, such as yachts, tugs and the like, the eiforts required for direct manual operation of the rudder, are generally too great to be convenient in practice. Follow-up controls for steering motors hitherto have been .relatively 'too eX- pensive to install on such comparatively small craft. Additionally, in many of such systems the operator was unable to .obtain a feel of the controlled mechanism.

It is among the objects of the present invention to provide a force amplifying follow-up systern in which a relatively large power is developed in response to the application of relatively small power, with the operator `retaining the "'feel ofthe controlled mechanism; `vto provide such a system in which a force responsive vdevice is inserted ina manually controlled lelement and controls the operation of a power mechanism in proportion to the direction and magnitude of the force exerted on such element; to provide such a system in which an electromagnetic force responsive device is incorporated with a manually controlled element and controls the operation of an electric motor operated mechanism in accordance with force exerted on the manually controlled element; to provide such a system including a manual operating mechanism, a power operated mechanism, an electric motor, electromagnetic torque responsive clutches, and means responsive to the force exerted on'the manually operated mechanism for engaging and disengaging such clutches with `a force exerted on themanually operated mechanism; and to provide a relatively simple, reliable, follow-up or servo-motor system having relatively few parts and which is accurately responsive to manually controlled force.

These and other objects, advantages and novel features of the present invention will be apparent from the following description and the accompanying drawing. In the drawing:

Fig. 1 is a diagrammatic illustration of the invention as applied to a steering system for a dirigible craft.

Fig. 2 is a diagrammatic illustration of a portion of the system shown in Fig. I, illustrating a modified form of the invention.

Fig. 3 is a diagrammatic illustration of another embodiment which the invention may assume in practice.

While the present invention is cap-able of many different applications, it will, for purposes of illustration, be described as applied to servomoter mechanisms. In accordance with the invention, a force responsive member is incorporated ina manually operated force transmitting means. The force responsive member preferably has a response of an electric nature, such as developing a predetermined voltage proportional to, or 'a certain function of, the lmanually applied force. Such voltage is used through the instrumentality of an electronic amplifier to effect operation of a power mechanism with a force proportionate to that exerted manually to operate the controlled element.

Preferably, the force yresponsive member cemprises an electromagnetic member inserted in `a control cable or rod and in which the magnetizing current through the element is proportional to the amount of tension -or pressure exerted on the element. Such Vpressure or tension may effect a variation in an 'air cap of Athe electromagnetic member or may exert a variation lin the magneto-strictive properties of the member. The variation in Vsuch Vproperties of the member effects a variation of the potential applied as the input to an electronic ampli-fier, e. g., a push-pull amplifier vto develop an amplied output controlling the engagement of one or the other of a -pair of velectromagnetic torque-responsive or slipping clutches connecting an electric motor to power driven devices for effecting control movements.

Referring to Fig. 1, the invention is illustrated as incorporated in a power steering arrangement for a controlled element, such as a rudder l0 which may be the steering element of ya water borne craft or an airplane. Rudder l0 is pivoted on a rudder stock Il to which is secured a cross bar i2. Cross bar l2 is operated vby means of force-transmitting means, such as cables having Vtheir respective ends rI?, and I4 wound respectively around power driven drums I5 and E6 and secured at Ytheir other `ends 13a and ld to force vresponsive members 2Q and 25 respectively. Such cables each have several'turns wrapped round their respective drums, the ends i3 and Ill being herein referred to yas the out put ends, and .the ends la and lila, as the "input ends. A `manually operated force- .transmitting means, such as cable l1 has each of vits ends secured Ato one of the elements 20 .or 25 and has several turns wrapped around the steering drum I8, being guided to the drum by suitable means .such as pulleys `2'| and 22. Drum I8 is secured for :rotation with a shaft 23 on the outer end of which is a suitable manually operated member, such as .a steering wheel '55. For a purpose to be described hereinafter, a 'braking drum 26 is mounted on the inner end of shaft 23 and adapted to be engaged by a vnormally disengaged, solenoid operated brake '21. A spring 28 normally urges brake -21 out of engagement with drum 26. Brake 21 may be engaged with the drum by closure of a, switch which connects a suitable source of current such as a battery 3| in circuit with a solenoid 32 operatively associated with brake 21.

The power operating mechanism includes an electric motor connected by leads 36 to a suitable source of electric current. Gearing 31 connects the output shaft of motor 35 to rotate a bevel pinion 38. Pinion 38 engages contrarotating bevel gears 4I and 42 secured to shafts 43, 44 respectively. Shafts 43, 44 are each connected to the driving members of one of a pair of electromagnetic torque responsive clutches or 45 which may be of the type disclosed in said Patent No. 2,267,114. Driven members of clutches 40 or 45 are connected respectively to drums I5 and I6. Normally, and as will later appear, clutches 40 and 45 are engaged. However, if the clutch currents are equal, rotation of pinion 38 and gears 4I, 42 by motor 35 is ineffective to operate drum I5 or I6, the clutches merely slipping.

In the arrangement shown in F'ig. 1, the force responsive elements 20 and 25 comprise C-shaped magnets having air gaps 45, 41 and provided with coils 5I, 52 around one leg of each magnet. Coils 5I, 52 each have one terminal connected to a suitable source of current indicated at which is preferably alternating current. The other terminals of coils 5I and 52 are connected, in series with resistors 53, 54 respectively, to the opposite terminal of source 50 which is grounded at 55.

Resistors 53, 54 are each connected across half of the input circuit of a duo-triode thermionic amplifier tube 60. For this purpose, dual cathode 6I is connected by a conductor 62 to the junction point of resistors `53, 54. The outer terminals of the resistors are respectively connected to the control grids 63, 64 of the tube. Anodes 56, S1 are respectively connected to one terminal of each of the electromagnetic clutches 40 and 45. The other terminals of these clutches are coinmonly interconnected to one terminal of a suitable source of current such as a battery 68. A pair of loss pass condensers 1I, 12 are connected across the output circuits of tube 60 to smooth the current flow through the electromagnetic clutches. The other terminal of source 68 is connected to dual cathode 6I. The foregoing arrangement constitutes a push-pull, i. e. phaseresponsive, amplier.

y The described arrangement operates in the following manner. Motor 35 is energized to continually rotate pinion 38 and gears 4I, 42. In the condition of the apparatus shown in the drawing, i. e. no force is being applied to the steering wheel, no rotation of drums I5 or I5 is effected as the current in clutches 40 and 45 are equal.

Magnets 20 and 25 are made of suitable resilient or elastic material, such as steel, so that a tension exerted thereon will vary the air gaps 46 or 41. It will be understood, however, that the magnets are of suchdimensions, and the material thereof so selected, that the elastic limit of the material is not exceeded. Otherwise the resultant permanent deformation would affect the working of the system. Moreover it will be understood that a change in the length or the air on the order of 0.010 may, by the use of a suitable electronic amplifier, produce a change in the current through the magnet coil suiicient to operate the clutch exciting winding. The preliminary adjustment is such that each of the devices 2IJ and 25 is preset under a moderate tension so that rotation of the wheel 65 will increase or decrease the respective air gaps from a predetermined normal.

Assuming that the rudder is amidships and that the helmsman is applying no eiort to the wheel 65 the tensions prevailing in input ends I3a and I 4a on the one hand and that in the output ends I3 and I4 will be equal. Also the gaps 46 and 41 and the reluctance of the magnetic circuits of devices 20 and 25 will equal. Accordingly the parallel circuits forming the respective inputs to the push-pull amplifiers described will carry equal quiescent currents, and the potential drop across each of the resistors 53 and 54 will be equal. Since this will result in v balanced output currents each clutch winding will carry the respective plate circuit quiescent current. However the output quiescent current may be selected low enough to maintain the clutches deactivated, or high enough to maintain the clutches in continued rotation. The latter is preferred in order that rotation of the clutches need not be initiated from standstill and interrupted at some frequency which will result in premature wear thereof.

With equal inputs to the two sides of the pushpull amplifier, and consequent equal outputs, both drums I5 and I6 will be rotated at the same speed and will be eiective to convert a force f on each input end I3a and I4a into a force F at each output end I3 and I4. But since f and F are both equal on both sides of the sys.- tem, there exists no resultant torque on the rudder I0. Assuming now that the helmsman applies an eiort to the wheel 65 in such a direction that a tension is applied to element 20, this will increase air gap 45 causing a corresponding increase in the reluctance and in the magnetizing current flowing in coil 5I. As a result, the potential drop across resistor 53 is increased and that across the resistor 54 is decreased. Upper half of the tube 65 will conduct more, and lower half will conduct less. Consequently the torque transmitted through clutch 40 to drum I 5 will be increased, and that through clutch 45 to drum I6 will be decreased. As a result the tension in cable ends I3 and I3a will be increased, and that in cable ends I4 and I 4a decreased, the increase and decrease being substantially equal in amount.

The tension in the cable ends I4 and I4a being reduced will permit a closure of the gap 41, a corresponding decrease in reluctance, and a reduced output from the lower side of the ampliiier. Clutch 45 will have its torque lowered and drum I6 will rotate at a speed slower than drum I5. This will result in predominance of the upper half .oi the apparatus, and the rudder will be rotated counter-clockwise.

From the foregoing it will be obvious that reverse movement of the steering wheel will cause clockwise rotation of the rudder, with the lower half of the apparatus taking the preponderant position.

With the invention arrangement the helmsman is able to simulate conventional direct manual steering, since, by exerting a weak effort the rudder may be maintained at a predetermined angle. To increase or decrease such angle requires only a corresponding rotation of the steering wheel and with a force just in excess of that required to maintain any then existing rudder angle.

In the event that the wheel 65 is left untended with rudder displaced from middle position, the present invention may act in two diiercnt manfaccdocp xners. iIf switch f30 v.is open .and thus 'brake 121 lis-'disengaged from drum 126,1the drum |.8 `and wheel 65 are free to turn `.under the v"effec'tfof :a

relatively-.small diiierence of tensions `existing in 'devices -2i) 'and25 duefto hydrodynamic 'pressure y'on 'the rudder |'0. r'Such relatively small AV'dif- Z'erence .Jin tensions "are =not`suicient to .modify Yappreciablythe air .-.gaps de and 'iii ttoefiect'fa) Apower operationof the mechanism.

rHowever, if it is desired to maintainapredetermined setting .of therudder, switch 3c 'is energized .to 'engage brake V21 with drum' 25 'and thereby fhold 'drum I8 stationary. Should the :rudderinow .tend .to 'turn .in a counterclockwise direction,.an increased tension will be exerted .on

.magnet "and Ja decreased tension onmagnet '20, The .potential'drops'.across resistors 53, 5li

determined relation. In the first case, -when brake 21 is released, .the action oi `wheel 65 vis exactly thesame as if lit'were directly Aconnected to 'rudder 1i). In the second case, the action is .the :same `as if a controlled moment were exferted lon wheel-65. From the precedingdescription it will be :apparent that a relatively small "braking force applied to brake drum 26 is capable of holding therudder at its predetermined angle.

Fig.\2 represents amodied form of thearrangement shown in Fig. 1, and lsimilar reference characters have been used to designate identical parts, In this arrangement, however, force responsive elements 1i! and 1G are inserted between .cable I1 and cables i3d and Ma in place of elements 2|! and 25. Elements y1li and 15 are loops of material having magnetostrictive properties, such as nickel. In such materials, the magnet permeability is altered under the effect of applied compression or tension.

Each `magnetic element 1B or 15 is provided with'a primary winding 1| or 12 which windings are connected in parallel across alternating current Vsource 5i) of substantially constant voltage. A secondary winding 13 or 14 is provided for each element 10,15, each secondary winding having one terminal vconnected to a control grid 63 -or 613 of tube 'B0 and th'e'other terminalconnected to ground 16 .andthro'ugh a biasing resistor 11 Vtodual'cathodeL The operation of .the circuit .shownin lFig. 2 is Ath'e'sam'e as that of 'the circuit lshown in lFig. 1. If 'a tension lis exerted on element 10, its magnetic permeability Ais V'changed eiecting a change in the .mutual inductance between the primary and secondary, van increase in 'its magnetizingv current and a correspondingly increased :potential 'impressed on grid "63. This 'in turn causes 'an increased output current to .be developed from anode 65 affecting engagement lof .clutch lil'to operate drum l5. A similareiect takes place when cable |'1 exerts a tension on Y magnetic .element 15.

While an velastic magnetic member, such Vas a steel magnet and a magnetic member having magnetostrictive properties have been illustrated las suitable force responsive elements, lother force responsive elements may instead be used. As such alternatives will be easily understood by `those skilled inthe art, they have not been illustrated in Yanfeiicrt to simplify the description of .thefinvention .applied force.

Figs. 1 and2 illlustrate the invention aslapplied 'lto steering mechanisms. AI-loweventhe invention 4is notlimited totsuchan application, :andiniay'fbe applied generally wherever an ampliedlforceis to be developed'in response to a-relativelysmall An alternative larrangement is shown in Fig. 3.

fInthe system of `Fig. 3, an electric motor 80-f2is provided with an 4armature shaft 8l :to ywhich'la pair Aof bevel pinions 82, '83 lare applie'd. The latter respectively drive 1.a pair of yloeve'lfpinions '84, -85 connected to the driving membersofa pair 4oi electromagnetic, torque responsive clutches 85, 81. Pinions 8S and 9D,:connectedre 'spectivelyto the driven elements of clutches 86 and S1 are arranged to rotate-a `gear i9j| `secured vto output shaft 52 in either direction. =Motor 180 is continually energized from 'a suitable source'of current through conductors V93. However, ordinarilyno rotation of pinions 38, 9i! or vgearlfoccurs as clutches Se and '81 aredisengaged.

Driving engagement of 'the clutches `is'eiected in the following'manner. A magnetic structure is shown as secured to a suitable xedfsupport such as a wall 95. Magnetic `structure -951com prises an E-shaped magnet having a base l51 from which projects an intermediate-or central arm 9B disposed betweenvthe inturned-.ends-of-a .pair of outer short arms lili), -ll providingair gaps |92, H33. A manually operable-.controlling member m5, such as a rod, is secured to-.armz98 to move the same'relative to arms |0,-|0| -ftovary the relative dimensions of air gaps 102,153. y

A pair of magnetizing windings -I-, |01 are mounted on arm 91 on either side of arm .98. One terminal oi each coil is connected to `a suitable source of Valternating current illustrated `at |08. Theother terminal of source mais grounded-at I0. The other terminals of coils |05 and j|01-are connected across source |98 to ground through resistors "l l I l2, respectively. i Y

of a duo-triode thermionic tube A|15. vDual cathode A| |6 `of tube |5 vis connected to @ground at ||1 and to the negative terminal of a suitable source of current such as a `battery .||-8. Anodes |28, |2| of tube |15 are each connected to a terminal of the energizing winding of .one of the clutches 8S or 31. The other 'terminals of the clutches are commonly interconnected .to the positive terminal oi source 1 i8. YLow'fpass condensers |22, .|23 are connected across both `halves of the output circuitof tube ||5 'to .filter alternating current components from the circuit including Vthe energizing windings of clutches 86 and 81.

The described arrangement otFig. 3 operates in the following manner. Assuming that a tension is placed on rod m5, air gap |92 willbe decreased and air gap m3 will be increased. Consequently, the voltage drop across resistor will be decreased and that across resistor l-2, increased. As these potentials are impressed on the 'control grids of tube ||'5,`the push-pull ampli'- iier will 4be activated to eliect 'a greater current -low to clutch B1 so that'motor 30 will drivefgear 8| 'and'shaft 92 through pinion 9i). 'The force exerted on shaft S2 will be proportional to the -force Aexerted. on rod |05 but will `-be greatly amplified with respect thereto. 'Rotationl of shaft 92 will `continue so long as :a tension is exerted on rod H33. A similar `effect takes Vplace A`in the opposite direction when compression is applied to rod IE5 to increase fair gap |02 and decrease air gap |03. It will be understood that, due to the nature of the push-pull amplifier here employed, the function will be similar to that described in connection with Fig. 1. That is to say, the quiescent current in each of the clutches 80 and 81 being equal, the gear 9| is, in the absence of a signal, forced to remain stationary.

The described invention provides a novel and simple servo-motor system in which a greatly amplied force is exerted proportional to a relatively small initiating force where the initiating force is manual, the operator retaining the feel of the control being performed. Complicated circuits and wiring are eliminated. If the arrangement is installed as a steering mechanism on water borne crafts such as yachts, tugs and so forth, no complicated mechanism between the pilot house and the steering motor is necessary, as all the electrical controls may be placed adjacent the steering motor. The force responsive members may be located at any point in the steering cable between the steering wheel and the power driven drums.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles thereof, it will be understood that the invention may be otherwise embodied without departing from such principles.

What is claimed is:

1. Torque amplifying apparatus comprising, in combination, a member for controlling a controlled element by the application to said member of a relatively small force variable in direction and magnitude; mechanism, including frictional clutch means and a source of power. for impressing on the controlled element a relatively large force variable in direction and magnitude; and control means for said mechanism including magnetic force responsive means operatively associated with said member; said control means continuously controlling the degree of engagement of said frictional clutch means to control the force exerted on the element by said mechanism in accordance with the direction and magnitude of the force applied to said member as measured by said force responsive means.

2. Torque amplifying apparatus comprising, in combination, a device for controlling a controlled element by the application to said member of a relatively small force variable in direction and magnitude; mechanism, including frictional clutch 'means and a source of power, for impressing cn the controlled element a relatively large force variable in direction and magnitude; and control means for said mechanism including electromagnetic force responsive means operatively associated with said member; said control means continuously controlling the degree of engagement of said frictional clutch means to control the force exerted on the element by said mechanism in accordance with the direction and magnitude of the force applied to said member as measured by said force responsive means.

3. Torque amplifying apparatus comprisingjin combination, a manually operable member for controlling a controlled element by the application to said member of a relatively small force; power drive means; electromagnetic clutch means operatively interposed between said power drive means and said force transmitting means; electronic means controlling the engagement of said clutch means; a linkage connected to said member for transmitting said force to a magnetic member forming a force-responsive elel0 ment in said linkage, said magnetic member having a reluctance variable in accordance with the force exerted by said manually operable member; magnetizing winding means on said magnetic member and connected in circuit relation with a source of power, the magnetizing current through said winding means varying in accordance with the reluctance of said magnetic member; and circuit means for varying the input to said electronic means proportionately to the change in magnetizing current through said winding means, whereby correspondingly to vary the output of said electronic means to vary the degree of engagement of said clutch means so that said power drive means will impress an amplied force on the controlled element proportional to the force applied to said manually operable member.

4. Apparatusl for amplifying a mechanical force for actuating a controlled element, comprising, in combination, a magnetic member having a reluctance variable in accordance with the force exerted on said member; a manually operated member for impressing on said member a relatively small force variable in direction and magnitude to vary said reluctance; mechanism for impressing a relatively large force on the controlled element; and electromechanical means, including a reversible servo mechanism and a phase-responsive amplier therefor, operatively connected to said magnetic member for controlling said mechanism in response to variations in said reluctance, to impress a relatively large force on the controlled element varying in direction and magnitude in accordance with the variations in direction and magnitude of the relatively manual small force impressed on said member.

5. Apparatus for amplifying a mechanical force for actuating a controlled element, comprising, in combination, a magnetic member having a reluctance variable in accordance with the force exerted on said member; magnetizing Winding means on said magnetic member and connected in circuit relation with a source of power, the current through said winding means varying in accordance with said reluctance; an element for impressing on said member a relatively small force Variable in direction and magnitude to Vary said reluctance; mechanism, including a source of power and electromagnetic slipping clutch means, for impressing a relatively large force on the controlled element; phase-responsive electronic amplier means controlling the engagement of said. clutch means; circuit means including said winding means for impressing on the input of said electronic means a potential proportional to the magnetizing current through said 'winding means, whereby to correspondingly vary the output of said electronic means to accordingly vary the engagement of said clutch means so that said mechanism will impress an amplified force on the controlled element proportional to the engagement of said clutch means.

6. A system for actuating the steering element of a dirigible vehicle comprising, in combination, a manually operable steering member; a steering dium connected thereto; a steering cable having an intermediate portion engaged on said drum and connected at both ends to the vehicle steering element; a pair of power driven drums respectively engaged with said cable on either side of said steering drum; a power drive means; reversing-type gearing means operable by said power drive means; a pair of electromagnetic slipping clutches respectively connecting said gearing" to each of said* power driven drums; phase-responsive electronic" means controlling tlieenergization of' said' clutches; a pair of magnetic" members respectively incorporated in said cableon either side of said' steering drumV and between'the saine and said power' driven drums; said' members having air'gapsvariable in accorda'nc'e" with forc'es'exertedy on said cable by said member or by the steering'element, and the reluctance of said members varying in accordance with thevariations in said air gaps; a pair of magnetizing' windings each respectivelyA associ'a'tedv with. one of said magnetic members and connected across a source of potential, the magnetizing current through said windings varying in accordance'with the reluctance' of saidy members; and circuit means for applying to said electronic meansva signal potential corresponding to the potential drop' across said windings, whereby said clutches.' will beV differentially energized to impress on" theY steering element, through said power driven drums, a force variable in direction and magnitude in' accordance with the direction and magnitude of the force exerted on said cable by said steering' device.

7.v Apparatus for amplifying a relatively small foret-:applied to' amanually operated member for actuation oi'a controlled element, comprising, in combination, a relatively xed magnetic member of` elastic material of E-coniiguration, the end legs/thereof' projecting toward each other to providean airg'ap and thecentral arm thereof being positionedin said air gap; said manually operated member being connected to said arm for impressing a relatively small force thereon to vary the position of said central arm in the air gap; a pairof Yma'gnetizing windings on said magnetic member'on either side ofY said central arm and' connectedacross a course of potential, the magnetizing' current through said windings varying in accordance with the relative position of said' central arm in the air` gap; mechanism, including', electromagnetic slipping clutch means, for. impressing a relatively large force on the controlled' element; phase-responsive electronic meansv controlling the energization of said clutches; .circuit means for applying to said electronic means. a signal potential corresponding to thecurrent through said windings, whereby said clutches Will be differentially energized to imf press" on ther controlled element an amplied force variable in direction and magnitude in accordance with the direction and magnitude oi the force exertedl on said central arm.

8. Ina system for controlling a controlled memoutput end, and circuitrv meanskv including said flux-producing means, anelectronic ampliier and servo-mechanism` for actuation of said power driven means in response to the'force measured by said measuring means, whereby a substantially proportional and continuousY relation between the input torque and the output torquemay be obtained.

9'. ApparatusiforA amplifying a relativelyl small force for actuation'of a controlled member with an' amplifiediversion of said'small force comprising'in combination an electromagnetic device including va core 'havinga gap'therein and a magnetizing winding, a member connected to said core'and: to which thesmalllforce may be applied for. varying', the reluctance of the magnetic circuit'proportionately tothe smallforce and thus to'vary the current'in'said winding, an electronic amplifier' having said winding connected in the input" thereof', aV powerv source, electrically-operated clutching means for connecting the controlled member to said source; said clutching means being. connected in the output circuit of saidamplier.

10.' lTorque` amplifying. apparatus comprising in combination a member forcontrolling a controlled element'by the application to said member of arelativelysmall force equivalent to an input torque, means including a deformable element and anv electrically conducting,` element,A means associated' with' said deformableelement, forcetransmitting means interconnecting said member and deformable`v element'. for translating movement or saidV` member` into'v a varying current through saidV electrically conducting element; power driving means, electricallyoperated clutch meansiorselectively'clutching. saidpower means to" said' controlled' element for" moving said controlled element pursuant to an' amplified' version ofA the input' torque; a current'. source, anv electronicamplier; andan'electrical circuit includingv said conductingv element, clutching means, am'pliercurrent source, formoving said controlled element pursuant to an amplified version ofthe-input torque;

NlCl-IOLAS MINOR'SKY.

REFERENCES CITED Thefollowing references are of record in the le of this patent.:

UNITED STATES PATENTS Number Name Date 654,130 Buck July 24, 1900 1,958,258 Alexanderson May 8, 1934 2,232,982 Tank Feb. 25, 1941 2,272,725 Overbeke Feb. 10, 1942 2,276,816 Bagno Mar. 17, 1942 2,294,906 Holloman et al. Sept. 18, 1942 2,348,211 Frische et al. May 9, 1944 2,385,351 Davidson Sept. 25, 1945 2,401,163 Kronenberger May 28, 1946 2,403,490 Black July 9, 1946 2,406,356 Davidson Aug. 27, 1946 2,421,626 Kuehni June 3, 1947 2,425,733 Gille etal. Aug. 19, 1947 

